1. Technical Field
The present invention relates to a recognition object detecting apparatus which detects a recognition object from an image taken by an in-vehicle camera.
2. Related Art
Conventionally, a technique is known which detects a predetermined recognition object from an image taken by an in-vehicle camera. For example, JP-A-2009-61812 discloses a technique in which an image of a scene ahead of a vehicle traveling at night is taken by using an in-vehicle camera. Next, tail lights of a leading vehicle or headlights of an oncoming vehicle are detected from the taken image as a recognition object. By using this technique, the control is realized under which headlights of an own vehicle are set to low beam if a leading vehicle or an oncoming vehicle is detected, and the headlights are set to high beam if a leading vehicle or an oncoming vehicle is not detected (auto high beam control).
Note that when a leading vehicle or an oncoming vehicle is positioned at a long distance from the own vehicle, luminance of the tail lights or the headlights in the image taken by the in-vehicle camera becomes lower and the image of the tail lights or the headlights easily disappears due to noise and the like, compared with a case where the leading vehicle or the oncoming vehicle is positioned at a short distance from the own vehicle. As a method for increasing accuracy in detecting tail lights or headlights at a long distance (low luminance), increasing the imaging sensitivity of the in-vehicle camera can be considered. However, as the sensitivity increases, the image of the tail lights or the headlights existing at a short distance (high luminance) is easily saturated in the image taken by the in-vehicle camera.
To solve the above problem, Japanese Patent No. 4034565 discloses a technique in which an image is first taken at low sensitivity, and another image is next taken at high sensitivity if tail lights of a leading vehicle or headlights of an oncoming vehicle are not detected from the taken image. That is, by performing imaging two times, accuracy increases in detecting the recognition object at both low sensitivity and high sensitivity. According to this technique, the lights of vehicles at a long distance can be detected despite the presence of noise and the like, while the lights of vehicles at a short distance away can avoid being saturated in captured images.
However, when performing imaging multiple times with changing imaging sensitivity as the conventional technique described above, the processing load substantially increases. The increased processing load causes a problem that the cost of manufacturing the apparatus increases and a problem that the miniaturization of the apparatus is prevented as the amount of heat generation increases. Note that such problems can be caused not only in the technique in which tail lights of a leading vehicle or headlights of an oncoming vehicle are detected as a recognition object but in a technique in which other recognition objects are detected.